Not Applicable
Not Applicable
1. Field of Invention
This invention pertains to optical switches. More particularly, this invention pertains to an array of optical switches with a spare input available to replace any of the optical inputs in the array. This invention also includes a method of actively aligning such an array.
2. Description of the Related Art
Optical signals are transmitted over fiber optic cables. There is a large demand to send optical signals over great distances without sacrificing data integrity. In order to achieve this goal, it is common practice to use repeaters at intermediate distances. Repeaters typically convert the optical signal into an electrical signal and then back into another optical signal, which is sent over the next length of fiber optic cable.
It is desirable to maximize the up-time of fiber optic systems. One common method to achieve maximum up-time is to have spare optical transmitters standing by that can be switched to replace failed transmitters. Typically, there is one spare for each transmitter, which results in a large amount of unused, standby capacity.
Fiber optic cables have a minimum bend radius which is large relative to the cable diameter. Accordingly, routing of fiber optic cables oftentimes determines the size and layout of fiber optic equipment, which is commonly rack mounted with input and output connections accessible from a front panel. In order to accommodate high density requirements, it is desirable to minimize the size of fiber optic equipment.
It is also desirable to minimize attenuation of the optical signals in optical equipment. A factor that affects attenuation is the dimensional stability of the components in the optical equipment. The optical signal from an fiber optic cable has a small size and small changes in alignment, for example, due to changes in temperature, may cause attenuation of the optical signal. Further, it is desirable to operate optical equipment over a wide temperature range, which is at odds with the desire to minimize attenuation.
According to one embodiment of the present invention, an optical switch assembly and method of assembly are provided. The switch assembly has a plurality of optical inputs providing optical signals to a plurality of optical outputs. The switch assembly includes actuators that can switch the optical signal from an optical transmitter to any one of the plurality of optical outputs.
The optical switch assembly includes an optical bench with input and output collimators fixed such that the optical signal is reflected from mirrors from each input collimator to its associated output collimator. In each optical path is an actuator that can redirect an optical signal from a collimator located at one end of the optical bench to the output collimator, thereby replacing a failed input signal with one from a single, spare laser. In another embodiment, the input and output collimators are reversed such that any one input can be switched to a single output collimator.
The optical bench is made of a material that has a coefficient of thermal expansion similar to that of the mirrors and adhesive fixing the collimators in place. In another embodiment, the adhesive is a fast setting compound that permits the collimators and actuators to be precisely positioned and fixed in place.
The method of actively aligning the collimators and actuators includes attaching the mirrors to the optical bench, positioning a first collimator, securing it with adhesive, and aligning the collimator. After the first collimator is aligned and fixed in place, the end collimator is similarly positioned, secured, and aligned. After the first collimator is aligned, the second collimator opposite the first is aligned by sending an optical signal from the first to the second collimator. After the first and second collimators are aligned, the actuator is positioned, secured, and the actuator mirror is aligned by sending an optical signal from the first to the end collimator. The above procedure is repeated for each pair of collimators.